The present invention relates to a respiratory waveform analyzer, and more particularly to a respiratory waveform analyzer which analyzes the respiratory waveform by detecting the concentration of a component in respiratory gas of the subject.
Various apparatuses and methods of monitoring the respiration of the patient who must undergo respiratory management in clinical practice or the like have been proposed. For example, the method which is called capnometry is known as a method in which a temporal change of the partial pressure of carbon dioxide contained in the expiration or the like, i.e., the concentration of carbon dioxide (CO2 concentration) in the expiration is measured to know the respiratory condition of the patient (for example, see JP-A-2003-532442).
As a method of measuring the CO2 concentration in the expiration of the patient, the photoacoustic spectroscopy, the mass spectroscopy, the Raman scattering spectroscopy, and infrared absorption spectroscopy (IR spectroscopy), and the like are known. Among them, the IR spectroscopy is known as a method in which expiratory gas of the patient is irradiated with light having the carbon dioxide absorption property, such as infrared light, transmitted or reflected light is detected, and the CO2 concentration in the expiration is measured from the absorption rate of the infrared light by the expiratory gas.
In a related-art capnometry, in the waveform of the CO2 concentration in the expiration, the maximum value of the waveform corresponding to one respiration of the patient is set as the effective concentration of the respiration, and detected as an end-tidal carbon dioxide concentration (ETCO2). In the case where the CO2 concentration in the expiration is measured by using the above-described IR spectroscopy, particularly, the problem is to improve the accuracy of detecting the ETCO2.
When the CO2 concentration in the expiration is measured by using an expiratory gas sensor of the mainstream type which is connected to a respiratory circuit to measure the CO2 concentration, for example, the inspiration of the patient is sometimes humidified. In such a case, it is often that water such as dew condensation water is reserved in the respiratory circuit. When such water is attached to a light irradiation portion or detection portion of the expiratory gas sensor in the respiratory circuit, the CO2 concentration cannot be correctly detected, with the result that the incorrectly detected concentration appears as noise components in the measured waveform. Then, it is often that a peak of such noise components is falsely detected as the ETCO2.
In the case where only expirations from the patient with respect to the air supply to the patient by a ventilator are to be counted as the respiratory rate, it is difficult to correctly remove the component of spontaneous respiration of the patient from the measured waveform.